Investigation of Mn dopant-induced crystal defects in photoactive CuSe nanosheets for enhanced visible-NIR range absorption and natural solar-driven photocatalysis.

Limited light absorption and inefficient charge separation remain key challenges in achieving effective natural solar-driven photocatalysis using low-bandgap CuSe nanosheets (NSs). Introducing crystal defects within a certain concentration range has been recognized as an effective strategy to tackle these issues and to design a high-performance photocatalyst. Herein, Mn is uniformly incorporated into the CuSe lattice, inducing crystal defects, resulting in efficient natural solar spectrum-driven photocatalysis. Photoluminescence (PL) spectroscopy revealed a systematic broadening in the full width at half maximum (FWHM) of defect-related emissions with increasing concentration of Mn-dopants, indicating the formation of defect states. Meanwhile, the conventional absorption spectrum indicated that without sacrificing the band gap, Mn-doped CuSe NSs exhibit improved visible and NIR-1 range absorption compared with the undoped CuSe NSs. Photocatalytic performance investigations, using methylene blue (MB) as a model dye, demonstrated a significant performance improvement. Results demonstrated that CuSe NSs with 9% Mn-doping showed 100% degradation with a degradation rate constant of 0.07 min, which was approximately 2 times that of the undoped CuSe NSs. This significant improvement in the degradation efficiency suggests that the Mn-induced crystal defects hold significant promise for the effectiveness of CuSe NSs in natural solar spectrum-driven photocatalysis.